I restored my helmets to as new, I've kept back a nice minty Fixed bale shell for myself, which had little or no combat use however the paint was well worn. This has been stripped and re-sprayed then re-corked while the paint was wet, and then sprayed again to seal the cork to the metal work.
What I will say is that if your replacing the webbing inside the liner this is not easy to do. The main problem is getting to the rivets to fold them over, in the finish I made a long reach punch and dye to do mine.
As to price, again I bought from another dealer in the states he had loads of M1 shell of all type's, approximately a 100,000 units and paid £20-£30 for each shell this include the fixed bale one. Helmets liners again came from another dealer and cost £15.00 each and most were the first run 1950's style with the eyelet in the front as per WWII production. I've got a late WWII Westinghouse liner which I will use with my fixed bale, as the Hawley liners are just to expensive to be even considered, plus are very easily damaged.